Process for treating crude pine tars



Patented Dec. 5, 1944 UNITED STATES PAT ENTOFFICE PROCESS FOR TREATING cnons rim;

, 'TARS Wiley C. Smith, Arlington, 1 Va.,' assignor it Claude R; Wickard, as Secretary of Agriculture of the United States of America, andto his successors in ofl'ice No Drawing. Application July Serial No. 400,881

3 Claims. (o1. etc-10v (Granted under the act of Mai-ch13, 1883, as v amended April 30, 1928; 3'79 0. G. 757) This application is made under the act of March 3, 1883, as amended by the act of- April 30, 1928, and the invention herein described and claimed, if patented, may be manufactured and used by or for the Government'of the United States of America for governmental purposes without the payment to me of any royalty thereonr" This invention relates to the ,treatmentlof crude pine tars to obtainmore' desirable products. 1t is particularly well adapted to the treatment of tars made by the kiln process.

An object of my invention is to remove from pine tar not only the dirt and othersolid extraneous mattenbut also bothfree and dissolved water. l l

Another object is to eliminatethe losses which resultfrom the usual distillation of tar.

' Still another object is to providea means of obtaining a purified tar having a desired viscosity and other prop'erties. Pine tars are obtained from thestumps and other resinous wood of the pineand certain other conifers byitwo general processes. In one process, the resinous wood iscarbom'zed in metal retorts. Tar and lighter volatile oils which are driven from thewood by the destructive distillation are condensed by cooling, and separated into rough fractions. The crude tar may be; distilled .to produce various "gradespof tars and tar oils.

A distillation of tar usually results in/anappreciablelosspby cracking with the formation of water and =uncondensed gases. ;Also the pitch which is formed bythe distillation is of less-value than are tars and tar oils. Tars made bythis percent of pyroligneous acid.

Pine tars are used inmarin'e paints, in treattar and pyroligneous acid. Crude kiln tars which have settled for aslong as 30 days may still *contain solid extraneous matter and several ing cordage, in compounding and reclaiming rubber, in disinfectants, and for a number of other purposes. The desired properties ofa tar w1ll varyaccordingto the use icrwhichit is intended. Tars 'may be jclassed in accordance with specific gravity and viscosity as thin, medium, and heavy; the-thin tar having the lowest spe- 3 cific gravity and viscosity." Retort'tars can he made to covera wide range inwiscosities by distillation and compounding. 3 Y s The composition andpropertiesof-kiln tar will vary somewhat dependingon the conditions of operation. The maker of kiln tar cannot conn01 closely the properties of his products. The presence of dirt and excess moisture in kiln tar yrstrictsits'use. The Navy Department specifies that pine tar shall be a high grade retort tar, free fromfdirtand foreign matter; other than water, which shall not exceed2 percentif The water is determined by distilling up to 200 C. Above 200 C. wateris formed by the cracking of certain constituentsbf the tar. This tolerance of 2 percent is to coverdissolved water.

process are commonly referred to as retort tars.

Inthe other process, the resinous wood is carbonized by subdued combustion in, kilns. Gases and light volatile oils escape into the air and are lost. The tar which isprod ucedruns through channels in the floor of the kiln into an outside pit orreceptacle. Tars produced by this process commonly are known as kiln tars. Tarsmade by a similar process insweden and other north European countries are known locally as valley tars. l

, Kiln tar as it is first produced contains large quantities of pyroligneous acid and certain solid extraneous matter such as sand, clay, charcoal,

etc. Before packaging, the tar is allowedto stand,

in :order that the heavy solids may ,settle and the pyroligneousacid may separate from tar and be withdrawn. However, this method is not 1 effective on a ccount of the viscosity of the .tar and t s a d ffe e dens t between; th

' atures willdissolve about 1.6 percent of water or pyroligneous acid. The removal of dissolved I have found that kiln tar at ordinary temperwater from pine tar will reduce-its corrosiveness to metaland enhance its value asa paint constituent.

changedronstituents of the oleoresin derived f rom th'e wood, and pyrogenatedproducts or" both i the oleoresin and thewood. The constituents of crudejtars include natural terpene hydrocarbons, isomerized and polymerized hydrocarbons, *resin acids, retene, wood phenols, pyroligneous acid, and various other substances, some of which have not been identified as yet. Crude reftars, except for the water and solid extraneous matter, while the'lighter petroleum distillates Crude pine tars consist of a mixture of unchloride, chloroform,

especially at the lower concentrations.

I have found that spirits of turpentine has a selective solvent action for .the constituents of tar which is difierent from that of the other common solvents and that the turpentine insoluble material (other than water and solid extraneous matter) has valuable properties. This turpentine insoluble material also has a higher specific gravity and a much greater viscosity than the original tars so that its removal will [reduce the specific gravity, and viscosity of the tar. A regulation of the removal of the quantity of this turpentine insoluble material will cause a variation in the specific gravity and viscosityof the tar. The addition of the lower boiling constituents to tar will cause a decrease in the specific gravity and viscosity of the tar. The diminution of the lower boiling constituents increases the specific gravity-and viscosity of the tar.

\ The process of treating crude kiln tar according to my invention consists, in brief, of the removal of the free water, undissolved solid extraneous matter, and a desired portion of the heaviest and most viscous component of the tar, which is followed by the removal of the dissolved water. i

Theword water covers the aqueous portion of tar which contains acids, phenols, and other substances, and is generally referred to by the industry as pyroligneous acid. This 7 aqueous liquid, or water, is heavier than pure water, and may have a specific gravity as highas 1.09, although it usually has a specific gravity of around 1.05, whereas the specific gravity of crude kiln tar is around 1.08, while that of crude retort tar may vary considerably.

It has been pointed out above that the high viscosity of crude kiln tar and the small density difference between this tar and the extraneous matter prevent an effective gravity separation or removal of the undesirable constituents. The

proper dilution of a tar with a suitable solvent will decrease its viscosity and change the density,

the insoluble portions have been separated from the diluted tar,the added solvent is removed by distillation. The dissolved water is distilled off along with the solvent. If a low viscosity tar is desired, the distillation is stopped as soon as the 0 added solvent has been recovered. If turpentine is used as a solvent, the distillation may be stopped before all the added turpentine has been recovered, the higher boiling portion of the turpentine remaining in the tar tends to reduce its viscosity and specific gravity.

If a more viscous tar is desired, the distillation may be continued after the added solvent has so that the extraneous matter will separate by gravity from the diluted tar. r

The general requirements of. a suitable solvent are that it be substantially insoluble in water;

that not more than asmall portion should distill above 175 0.; and that it should have a specific gravity widely divergent from 1.05. Its desired solvent power will depend to some extent on the properties ofthe treated tar. As an example, if a heavy tar-of the cordage treating type is required, the solvent used for thinning the crude tar to separate the fwaterfl and solid extraneous matter, should precipitate a minimum of the heavy, viscous portion of the tar. For most purposes, however, a tar from which some of the turpentine insoluble portion has been removed is example, coal tar hydrocarbons, petroleum dis uniform composition, and had a viscosity apbeen recovered until the temperature has reached as high as 200 0., thereby'removing some of the lighter and lower boiling constituents of the tar, which may be collected separately, These lower boiling constituents, which'were removed by the continued distillation, may be added to other ta s to reduce further their viscosity and specific gravity. Turpentine and, other higher boiling solvents, on removal from the diluted tar, by distillation, carry over a small quantity of phenols.

These phenols may be removed by washing the solvent with aqueous sodium hydroxider The re;

covered solvent may be repeatedly usedwithout removal of thephenols.

The dilution and settling of the crude tar niay be carried out in a manner similar to that which crude pine gum and analogous materialsare theoperation of the process embraced by, my invention: s s

Onevolume of spirits of turpentine '(sp. gr. 0.86 at 25 C.) may be added, with stirring, to one volume of crude kiln tar (sp. gr. 1.08 at 25 0.). The mass may be stirred until maximum solution is effected and then allowed to stand overnight, or i foratleast two hours,- or .until suchtime as the diluted tar separatesfrom the water, trash, etc. The diluted tar mayibe placed in a still and heated to substantially 150 0. when steam maybe injected, anddistillation byflsteam carried on until the solvent recovered equals substantially of thesolvent-addd. The steam injection-may be discontinued, and

the temperature of the tar 'raised-to-170 C. to

drive outany residual water. This dilution will cause'a separation of the free water 'and'a greater part of the insoluble portion of the tar.

The tar resulting from the above process contained no free and/or dissolved water; was of preaching a thin tar, whiletheoriginal tar wouldbe classed as "heavy." The use of a greatfer proportionof turpine for dilution would have precipitated a greater quantityoi? viscous materialfrom the crude tar and resulted in a; less viscousrefined tar. .The, dilution or the crude v kiln tar with an equal volume of low boiling coal tar oils would cause a separation of but a small part of the viscous portion of tar and the refined tar would beclassedas heavy.

While it is not possible to specify the exact quantities of thevarious solvents to use for dilution, nor the maximum temperature to which the distillation for removal of added solvent should be carried, in general, dilution of the crude tar with an equal volume of solventis deemed in the production of a water-free refined prod-,

not, which comprises adding to crude kiln pine tar an equal volume of a petroleum distillate distilling below 175 C., thence agitating the mass; thence separating the diluted tar from the wadriving olT the added solvent and dissolved water, and thence recoveringthe residue as a water-free refined product.

2. A process for treating crude kiln pine tar in the production of a water-free refined product, which comprises adding to crude kiln pine tar an equal volume of a coal tar distillate distilling below 175 0;, thence separating the diluted tar from the water and other insoluble material present, thence distilling the dilutedtar up to 170 0., thereby driving off the added solvent and dissolved water, and thence recovering the residueas a water-free refined product.

3. A process for treating crude kiln pine tar in the production of a water-free refined prodnot, which comprises adding to crude kiln pine tar an equal amount of spirits of turpentine, thence separating the diluted tar from th water and other insoluble material present, thence distilling the diluted tarup to 170 0., thereby driving off the added solvent and dissolved water, and thence recovering the residue as a Wa ter-free refined product.

WILEY C. SMITH. 

